When you mark an alert as unseen, the corresponding alerts icon changes to indicate the presence of the alert (if another unseen alert of the same or higher severity is not already outstanding). The icon of the system to which the alert applies changes from its normal appearance back to the appearance appropriate for the severity of the alert, if an unseen alert of the same or higher severity has not already been raised for this system.
To mark an alert as unseen, do one of the following:
Remove the check mark in the Seen column for the alert.
Right-click the alert and click Mark Unseen from the shortcut menu that appears.
In the Alerts window, click the alert in the alerts pane, and then click Mark Unseen on the Edit menu.
You can also mark multiple alerts as unseen at one time by selecting all of the desired alerts and performing one of the above methods.